A popular autofocus camera having a lens shutter performs automatic focus detection which generally relies on the principles of triangulation near the viewfinder in a path differing from the photographical path. In practice, the camera lens is set at a given position according to the results of the detection.
Meanwhile, a single lens reflex (SLR) camera equipped with a focal-plane shutter automatically adjusts the focus with high accuracy, because the error associated with the lens-driving portion is accommodated, which arises from the fact that the lens is brought into focus by focusing the light rays which pass through the lens.
On the other hand, a camera having a lens shutter is more advantageous than SLR cameras in flash photography. Further, the former camera is excellent in portability. Therefore, cameras having a lens shutter have enjoyed wide acceptance.
In recent years, multifocal cameras and cameras having a zoom lens have gained popularity. With these cameras, a method adopted to bring the camera lens into focus involves measuring the distance externally when the lens is used at a longer focal point. The camera lens is focused according to the obtained value. In this method, errors arising during setting and errors intrinsically present in the lens system cannot be neglected. Hence, each step of the manufacturing process requires that adjustments be made with excessively high accuracy.
In view of the foregoing, the invention seeks to provide a camera which has a lens shutter but provides automatic focus adjustment equivalent to the adjustment in an SLR camera, thereby accurately adjusting the focus.
In a camera equipped with a lens shutter, the optical path of the camera lens is closed before operation. Therefore, it is impossible to know whether the light rays transmitted through the optical path are focused.
Accordingly, the provision of a separate means which shields the image plane to be photographed may be contemplated to enable the lens shutter to open. However, to achieve complete shielding, large shielding members such as a pair of focal-plane shutters are required, thus rendering the structure complex.
The present invention enables adjustment of the focus by focusing the light rays which pass through the camera lens. The invention also provides that the image plane to be photographed is completely shielded by a simple method.